Critical Vulnerability Patched in GnuPG, Libgcrypt

The GnuPG Project announced last week the availability of GnuPG and Libgcrypt updates that address a critical security problem affecting all versions released over the past 18 years.

GNU Privacy Guard, also known as GnuPG and GPG, is a free implementation of the OpenPGP standard. Offered as an alternative to the PGP cryptographic software suite, GPG is used by several applications, including popular email encryption tools. Libgcrypt is a general purpose crypto library based on GPG.

Researchers Felix Dörre and Vladimir Klebanov from the Karlsruhe Institute of Technology in Germany discovered a problem in the mixing function of the Libgcrypt pseudorandom number generator (PRNG).

“Due to the flaw, mixing the full entropy pool reduces the stored entropy amount by at least 20 bytes. Furthermore, the flaw makes a part of the PRNG output completely predictable,” the experts wrote in a paper detailing the issue.

According to Werner Koch, the developer of GnuPG, an attacker who obtains 4640 bits from the RNG can easily predict the next 160 bits of output.

“A first analysis on the impact of this bug in GnuPG shows that existing RSA keys are not weakened. For DSA and Elgamal keys it is also unlikely that the private key can be predicted from other public information. This needs more research and I would suggest _not to_ overhasty revoke keys,” Koch said in a security advisory.

The vulnerability, tracked as CVE-2016-6313, affects all versions of GnuPG and Libgcrypt released since 1998. The issue has been resolved with the release of Libgcrypt 1.7.3, 1.6.6 and 1.5.6 for GnuPG-2 2.0.x and 2.1.x, and GnuPG 1.4.21 for GnuPG-1 version 1.4.x. Software projects using GnuPG and Libgcrypt are expected to release updates of their own.

GPG hit a rough patch in 2014 due to the lack of funding. However, Koch managed to attract the attention of the media, which resulted in tens of thousands of dollars in individual donations and a one-time grant of $60,000 from the Linux Foundation’s Core Infrastructure Initiative. In addition, Facebook and payment processor Stripe pledged to donate $50,000 per year to help sustain the project.

Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.